(a) Field of the Invention
The present invention relates to an apparatus and method for operating a (wireless access in vehicular environments) WAVE-based multi channel.
(b) Description of the Related Art
In a wireless network, when several communication nodes shares one radio channel, if two or more communication nodes simultaneously uses a radio channel, collision occurs and thus communication cannot be performed. In order to lower probability of such collision, a communication node uses a carrier sense multiple access with collision avoidance (CSMA/CA) method using a random backoff time.
In the CSMA/CA method, when a communication node has data to transmit, the communication node grasps an occupying state of one radio channel, and when a radio channel is in an idle state, the communication node transmits data. If a radio channel is not in an idle state, the communication node sets a random backoff time and checks the radio channel while reducing a random backoff counter value according to the random backoff time. In this case, when a backoff counter value according to a random backoff time is 0, if a radio channel is an idle state, the communication node transmits data.
In this way, in one physical layer, when a channel occupying ratio of communication nodes is not high, a CSMA/CA method based on one radio channel, i.e., a single channel has low collision probability and thus the single channel-based CSMA/CA method is efficient. However, as the quantity of communication nodes increases and a data amount to transmit increases, a use frequency of a network increases and the network becomes complicated, and thus probability to cause communication delay and communication failure increases due to packet collision.
Communication environment between vehicles has characteristics that the quantity of communication nodes frequently changes according to the quantity of vehicles even in the same range. Particularly, in an area having a high density of vehicles, such as a downtown area or a roadside intersection, a situation in which a plurality of communication nodes simultaneously perform communication frequently occurs. Therefore, a single channel-based CSMA/CA method may cause frequent communication delay and communication failure in communication environment between vehicles.
Further, in the CSMA/CA method, a priority order is not provided to data to send. Therefore, transmission delay of emergency data to urgently transmit in real-time may occur.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.